1. Field of the Invention
This invention relates to pneumatically operated valves and, more particularly, to safety valves for noxious-gas cylinders.
2. Prior Art
In the field of industrial uses of gases under pressure a primary problem is the prevention of undesired leakage from the cylinders in which those gases are stored under pressures in the order of 2500 p.s.i. Because of the complexity of present-day valves used for this purpose, they tend to leak due to sticking of moving parts of the valve, particularly after extended use. Further leakage occurs when connection of the conventional valve to the gas distribution system is not tight. The leakage problem is particularly critical in the field of semi-conductor manufacture where such flammable and toxic gases as silane, phosphine and arsine may be stored in the cylinders for use in the manufacturing process. Such gases may also be corrosive and, in general, are extremely injurious to human health, even in small concentrations. With the increased emphasis on safety and the proliferation of personal injury and worker's compensation litigation it is imperative that any accidental release of noxious gases to the environment be eliminated. Prior art valves (globe valves) typically locate their poppets so that inlet pressure opens the valve. This may result in dangerous leakage of noxious gas.
Further, in coupling the valve outlet to the first nipple of the gas distribution system it is not uncommon for such nipple to be less than fully seated in the valve output port with the result that gas escapes at that joint.
Therefore, it is a first object of this invention to overcome the general objections to prior art safety valves.
It is a further object of this invention to provide a pneumatically operated safety valve with minimum complexity, maximum freedom from gas leakage and maximum freedom from failure over an extended period of usage.